Can you solve these questions ASAP ? Write the names of all possible pyroxenes i

Question

Can you solve these questions ASAP ? Write the names of all possible pyroxenes in their proper place on the accompanying ternary diagram. Write a basic (structural) pyroxene formula and then write the cations (no Si or O) for each mineral directly underneath their location. Include all tielines and regions of solid solution. Write General Pyroxene Formula Write the names of all possible amphiboles in their proper place on the accompanying ternary diagram. Write a basic (structural) amphibole formula and then write the cations (no Si or O) for each mineral directly underneath their location. Include all tielines and regions of solid solution Write General Amphibole Formula Pyroxenes and amphiboles have limited solid solution between certain endmembers. So- Why? A) Why only limited? Why only certain endmembers? B) Discuss why a definition of solid solution explains the specific types of solid solution evidenced by the pyroxenes and amphiboles. Check, of course, that it does. Think first. C) How is this notion of solid solution evidenced by the physical properties? Could physical properties alone lead us to the notion of solid solution? List some physical properties (in the pyroxenes and amphiboles) that are affected by solid solution. Some drawings Draw schematic diagrams and explain the two main "I-Beam" structures of the Inosilicates. Include the location of all "M" and "T" sites (and the pointing direction of the tetrahedron apices). List and/or briefly describe how these different structures affect physical (measureable) properties by identifying the property and how it changes. I-Beam Structure I-Beam Structure Properties Properties Draw a typical view (cross-section) looking down the c-axis- showing diagnostic cleavages. Label each prominent face with its Miller Index (use the proper type of bracket) Does this notion of an I-Beam as a structural element relate to any other silicate classes? Explain.

Explanation / Answer

1. The vast majority of natural pyroxenes fall within or near the 'pyroxene quadrilateral'. Substantial solid solution exists between Enstatite(Mg2 Si2O6) and Ferrsilicate(Fe2Si2O6). Complete solid solution occurs between Diapside(CaMgSi2O6) and Hedenbergite(CaFeSi2O6). So in the quadrilateral diagram the following pyroxenes are present:

a.Wollastonite (CaSiO3)

b. Diapside(CaMgSi2O6)

c.Hedenbergite (CaFeSi2O6)

d. Enstatite (Mg2 Si2O6)

e. Ferrosilicate (Fe2Si2O6)

f. Augite (intermediate between Diapside-Hedenbergite )

g. Pigeonite ( Intermediate between Augite and Enstatite)

The basic formula of pyroxene is XYZ2O6

where, X = Mg, Fe2+, Ca, Na, Li, Mn

Y= Mg, Fe2+, Fe3+, Mn, Al, Cr3+, Zr

Z= Si with substitution by Al and Fe3+

Those that crystallize in orthorhombic space groups are collectively called orthopyroxene (opx), while the high-calcium pyroxenes are the clino[yroxenes(cpx).

The crystalline structurte of pyroxene minerals consist basically of silica-tetrahedra linked in the form of chains by sharing of two basal oxygens between neighbouring tetrahedra. The other important cations like Mg2+, Fe2+, Ca2+ occure as larger cations that are linked to the chain by oxygens to form the total pyroxene structure.

The general pyroxene formula- CaSiO3 (opx) and XYSi2O6 (cpx).

2.Amphibole group is classified on the basis of dominant X-cations

i. Fe-Mg amphibole

ii. Sodic(Na) amphibole

iii. Calcic (Ca) amphibole.

Among these, Fe-Mg amphiboles are the most uncommon in nature while calcic amphiboles are the most common.

Fe-Mg amphiboles: Anthophyllite, Gedrite, Holmquisite, Cummingtonite, Grunerite.

Sodic amphibole : Glaucophane, Riebeckite, Magnesioriebeckite.

Calcic amphibole : Tremolite, Ferro-actinolite, Common Hornblende.

The generalized formula of amphiboles is

W0-1 X2 Y5 Z8 O22 (OH, F, Cl)2

In this formula Z represents Si. These are in tetrahedral co-ordination in the double chains (the T-site). The X and Y cations are located in octahedral sites. Y corresponds to Mg, Fe2+. Fe3+, Mn, Al and Ti. The X cations are Na, Ca, Fe2+, Mg, Mn and Li. The W cations, when present occupy the A-site and usually consist of K and Na.

The general amphibole formula is (Ca, Na)2 (Mg, Fe, Al)5 (Al, Si)8 O22 (OH)2

3. If we observe the pyroxenes and amphiboles phase diagrams, there are complete solid solutions between the end-members due to complete solubility between the members, but certain members show limited solid solution because of limited solubility in both liquid and solid states.

4. A specific type of solid solution occurs in pyroxene group is Mg-Fe solid solution i.e. between Enstatite and Ferrosilicate minerals. For amphibole, the solid solution occurs between Na and Ca cations and between Mg and Fe. Example is Anthophyllite and Grunerite solid solution.

Related Questions

Navigate

• Browse (All)
• Browse C
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.